Most "unbranded" autos aint great tho man, Iv bought unbranded Low-berrys and such and they just aint as "stable" as you'd hope. You should try Easyryder (AK47 x Lowryder#2) by the Joint Doctor, soaring head high and between 1 and 2 zips a plant of delicious smelling, tasting, potent stuff. I put mine under a 400w HPS on 18/6 the whole way through and mine are awesome! Hope this helps.
EDIT: You dont have to switch spectrums, they go from seedling straight to flower so your wasting time/money for the tiny bit of stretch you'll see and also the 6 weeks usually isnt from seed to harvest, its usually the flowering period. Most autos average 8 weeks from seed to chop. Again, hope this helps!